Tris(2-hydroxyethyl)isocyanurate (THEIC) is a triol used extensively to improve the performance of polyester-based magnet wire enamels. Electrical insulation made with THEIC polyesters of adipic, phthalic, isophthalic, terephthalic and similar polyacids exhibit good dielectric properties, and show improved adhesion, flexibility, heat shock, and heat aging performance.
THEIC is commercially prepared by reacting isocyanuric acid with ethylene oxide in an inert solvent and in the presence of an alkaline catalyst (normally an alkali metal hydroxide). Although good yields are obtained, the method is not without problems. Ethylene oxide, which is a gas at room temperature and pressure, is an acute and chronic poison, as well as an explosive hazard, and therefore difficult to handle safely. Furthermore, the reaction product must be purified before it can be used in a magnet wire enamel. Impurities (especially cations) will increase the electrical conductivity of the electrical insulation, and may also interfere with formation of the polyester and contribute to premature decomposition of THEIC.
Purification is an involved process. First, the solid catalyst and any metal salt by-products are removed by filtration. Next, the filtrate is distilled under vacuum to separate out the inert solvent, leaving a viscous residue (THEIC). Finally, the THEIC is re-dissolved in a volatile organic solvent and then recrystallized yielding THEIC sufficiently pure for use in magnet wire enamel.
It is therefore desirable to prepare THEIC without the handling problems associated with ethylene oxide, and without the need for extensive purification of the reaction product prior to its use.